About half way up Leg 3 of Race 8 today, Emirates Team New Zealand tacked to leeward of Oracle Team USA. They did not have sufficient pressure in the hydraulic system, and the 14 metre wide catamaran came close to capsizing as the wingsail failed to flip onto the new tack.

Many have had concerns about the viability of the AC72 catamaran for sailing at this level. Today underlined they are maybe too close to the edge.

Hydraulics are not new to sailing at this level, but most boats that do use them extensively are running small engines to provide the required hydraulic pressure. The AC72’s rely on grinders. It takes four grinders to produce the same horse power of a sewing machine – about 2hp – and that’s before the lactic acid kicks in.

So it is small wonder that there was a incident arising from a lack of pressure in the on-board systems.

Emirates Team New Zealand rounds mark one in the lead over Oracle Team USA. Race eight on day five of the America's Cup 34. 14/9/2013

The way it was explained at the media conference, a cam belt comes into play when the boat tack – cracking the 40 metre high wingsail out of its old shape, and into the new, as the boat tacks.

Lack of pressure mean that the cam belt wouldn’t move quickly enough, and the wingsail retained its old shape triggering a capsize situation. Fortunately the grinders had the presence of mind to keep winding as the opposite hull towered above them – eventually getting enough pressure in to the system to grind the wingsail through to its new shape. As skipper Dean Barker explained not a split second too soon.

But the drama caused audible cries of 'Oh no' on the water, and Kiwi fans could only watch and hope for the miracle which happened, saving a catastrophe.

Most would have been quite happy to emerge from the race in second place, and with the wingsail intact. Had the boat gone over and suffered major damage, the second Kiwi boat is substantially slower and that would have made a come from behind Oracle Team USA's successful defense much more likely.

Oracle Team USA v Emirates Team New Zealand. America's Cup Day 5 San Francisco. Golden Gate Yacht Club

As it was Oracle Team USA emerged from the day in much better shape than most had expected. Rather than clocking up a couple more losses, they came out with a win, and took heart from an improved performance against the New Zealanders.

One thing that does seem noticeable is that Brit-Australian tactician-strategist roles at the back of the boat, with Ben Ainslie and Tom Slingsby seems to be working more smoothly.

However the USA team lost both their starts against the Challengers – an area in which they had previously been dominant in the regatta.

They rounded the leeward Mark 2 behind NZL5 on both occasions, and although they did make an impression on the Kiwis on the windward beat which has normally been their nemesis. New Zealand led at the time of their near capsize, in Race 8, and were also ahead when Race 9 was abandoned.

Oracle Team USA v Emirates Team New Zealand. America's Cup Day 5 San Francisco. Emirates Team NZ comes close to a capsize in Race 8 as Oracle Team USA avoids